Electrical laminates products, which are used in making printed circuit boards, typically comprise a multilayer assembly of a thermoset epoxy resin matrix in a reinforcing fiber glass mat. Printed circuit boards are typically perforated by drilling holes in the board to provide the solder connections on the board. Typically, electrical laminate products, such as those made from epoxy resins, have a high thermal resistant but are highly cross linked and display brittleness. It is therefore necessary to assess the drillability of such laminates made from various epoxy resin materials to determine if such laminates will adequately pass the rigors of the drilling step in the process of making printed circuit boards.
The performance of laminates is the result of the combination of the fracture properties of the epoxy used to make the laminate, the stiffness of the assembly and the adhesion of the epoxy matrix to the reinforcing fiber glass mat. Delamination of the layers which make up a laminate reveals a detrimental propensity of the laminate to propagate cracks when under localized pressure. There is an urgent need in the epoxy industry for a high temperature epoxy resin because of the use of such resins in lead-free soldering processes in the industry. However, a major concern is that by increasing the temperature of degradation of an epoxy, it also increases the brittleness of the epoxy. Brittleness can cause delamination and chipping of a laminate during drilling procedures. There is a need in the epoxy industry for an easy drillability testing or screening method.
Drillability of epoxy laminates is currently assessed through a costly testing process including drilling fabricated laminates using actual expensive industrial-sized laminate drilling machines. Access to such laminate manufacturer's drilling machines is not readily available. It may also take a long time to obtain such drillability results because it requires the analysis of a large number of small drilled holes on highly magnified pictures. The inaccessibility of the drilling machines makes it hard for raw material suppliers, such as epoxy resin producers, to examine the true performances of a final composite, made from a formulation of raw materials.
“Drillability” of epoxy laminates is characterized by the lifetime of a drill bit, that is, the number of hits the drill bit can survive before breakage. Another method of characterizing the “drillability” of an epoxy laminate is the wear of the drill bit over the number of hits, the wear being characterized as flankwear. These quantitative estimates are done using a laminate drilling machine.
The industry is still looking for an inexpensive way to test samples of laminates easily and quickly in order to make an efficient and a quick determination of the machinability of electrical laminates. Therefore, it is desired to provide a device and method of testing laminates. It is desired to provide a device and method for assessing the drillability of a sample of a laminate that does not require the actual drilling of the sample. It is also desired to provide a device and method that can provide a measurement of the performance of an epoxy resin from a sample of a laminate made from such epoxy resin without using a drilling tool.
It is further desired to provide a low-cost, quick method of assessing the machinability of epoxy laminates (i.e. drillability, routing, sizing and cutting) made with any epoxy resin formulation, particularly from epoxy resins having a high degradation temperature. The prior art does not teach or disclose such a low-cost quick method to screen formulations for making electrical laminates. The prior art only discloses full-scale drilling tests requiring a time-consuming trial.